The present invention relates to power supplies and more particularly to contactless power supplies capable of supplying power to a variety of portable devices.
Contactless power supplies transfer electrical energy to one or more portable devices without mechanical connection. A typical contactless power supply drives a time-varying current through a primary coil to create a time-varying electromagnetic field. One or more portable devices can each include a secondary coil. When the secondary coil is placed in proximity to the time-varying electromagnetic field, the field induces an alternating current in the secondary coil, thereby transferring power from the contactless power supply to the portable device.
In order to increase the power transfer from the contactless power supply to the portable device, it is generally desirable to increase the coupling coefficient between the primary coil and the secondary coil. At the same time, it can be desirable to provide power to the secondary coil across multiple positions and orientations with respect to the primary coil. These goals are often in tension. That is, achieving a high coupling coefficient can confine the portable device to a single location on the contactless power supply, while maximizing spatial freedom can lower the coupling coefficient, and therefore the power transfer, to undesirable levels.
Stated somewhat differently, contactless power systems using coupled electromagnetic fields have become increasingly common in commercial applications. It has been demonstrated that the efficiency of any system that transfers power through inductively coupled coils is inversely proportional to the spatial separation between the center point planes of those coils. However, the non-trivial expectation of spatial freedom of subsystem placement while maintaining efficient energy transfer between the coils of the transmitter and receiver subsystems has become a major focus area of this technology. Achieving this challenge has been a major topic of contactless power systems research. Approaches by some researchers allow the perception of arbitrary positioning through the selective combination of small coils. This approach can require a significant number of coils and corresponding control electronics to supply power to an arbitrarily large area. Another approach delivers power to an arbitrarily large area but can require inductors of very high Quality Factor. Furthermore, this type of system solution can be difficult to control in the transfer of energy into arbitrary devices that are in the transmitter-generated field.
A number of additional contactless power supplies have attempted to provide some degree of spatial freedom to the portable device, while also maintaining an acceptable coupling coefficient between primary and secondary coils. For example, one known contactless power supply includes an array of vertically-oriented primary coils in parallel alignment with one another. That is, the primary coils are oriented in side-by-side relationship with corresponding central axes being perpendicular to a power transfer surface. An orthogonal secondary coil can be positioned lengthwise above first and second primary coils in the array, having a central axis parallel to the power transfer surface. The first primary coil can be energized with a first polarity, while the second primary coil can be energized with a second polarity. The two primary coils generate a cooperative magnetic flux in the region occupied by the secondary coil. If the portable device is moved along the contactless power supply, one or more different primary coils can be energized to again provide two underlying primary coils having an opposite polarity.
Despite the advantages of the above system, such an array can be expensive to manufacture, and can include a high-profile cross-section depending on the height of each primary coil in the array. In addition, the process of winding and assembling an array of primary coils in this arrangement can be cost prohibitive in some applications. Accordingly, there remains a continued need for an improved contactless power supply for providing power to one or more portable devices. In addition, there remains a continued need for a low-cost contactless power supply to supply power to one or more portable devices across multiple positions and orientations on a power transfer surface.